Bone condition in children with juvenile idiopathic arthritis

Abstract

Osteopenia (osteopenic syndrome) and osteoporosis (OP) are among the frequent and highly disabling conditions that accompany the development of rheumatic diseases (RD), including juvenile idiopathic arthritis (JIA). Changes in the requirements for the diagnosis and treatment of children with JIA according to the treatment strategy to achieve the goal (treat to target) have led to a decrease in the frequency of development and manifestations of OP in patients with RD. The condition of bone tissue in children with JIA, against the background of modern therapy and in conditions of widespread vitamin D deficiency requires further study.

Purpose — to study bone mineral density (BMD) in children with JIA in modern disease management and to identify adverse factors for the development of OP among clinical signs.

Materials and methods. We examined 35 children with JIA aged 7 to 17 years, mostly female (77.1%), with oligo (25.7)%, poly (60.0%) and undifferentiated (14.3%) option, 53.4% of whom have not yet received basic therapy. All patients underwent BMD by dual-energy X-ray absorptiometry on a bone densitometer Explorer QD W (Hologic), parathyroid hormone (PTH), 25-hydroxyvitamin D [25(OH)D], total and ionized calcium and phosphorus in syvo. The control group consisted of 12 healthy children of the same age with a normal level of 25(OH)D.

Results. The mean level of vitamin D in the serum of children in the main group was 20.41±1.35 ng/ml, which was significantly lower than in the control group (30.03±2.53 ng/ml, p<0.05); the frequency of low levels of vitamin D reached 88.57%. The content of calcium and phosphorus in the blood did not deviate from the normative values, despite the widespread deficiency of vitamin D. 98.37% of patients had normal PTH values, the average level in the blood was 30.43±0.90 pg/ml. The content of PTH was the highest in non-differential arthritis (34.33±1.80 pg/ml), the lowest in the oligoarticular variant (28.36±1.43 pg/ml, p<0.05). PTH concentrations correlated with vitamin D levels (r=-0.41; p<0.05) and were independent of patient gender and disease activity. The frequency of decreased BMD was 28.57% of the surveyed children. The prevalence of osteopenia was the same in different variants of arthritis and did not depend on the sex and age of patients, positivity in the RF. Osteopenic syndrome was significantly more common in ANA-positive JIA than in ANA-negative variant (46.15% vs. 18.18%; pϕ<0.05). The condition of bone tissue (Z-criteria) depended on BMI (r=0.33; p<0.05), disease activity on the JADAS scale (r=0.35; p<0.04), the number of active joints (r=0.34; p<0.05); ANA level (r=-0.34; p<0.05). In the group of children with osteopenic syndrome, BMD correlated with the duration of the disease (r=-0.67; p<0.05), the number of active joints (r=-0.62; p<0.05), the level of blood phosphorus 0.74; p<0.05) and the sum of points on the JADAS scale (r=0.59; p<0.05). In the group of children with preserved BMD, the spectrum of correlations was supplemented by indicators of vitamin D status (r=-0.33; p<0.05) and BMI (r=-0.40; p<0.05).

Conclusions. In children with JIA, the incidence of osteopenia is 28.57% with vitamin D deficiency in 88.57% of patients, preserved levels of total calcium, phosphorus and PTH in the blood. Decreased BMD in the early stages of JIA is associated with a younger age of patients and the age of onset of the disease, increased prevalence of joint syndrome, inflammatory and serological activity of the disease, ionized calcium and blood phosphorus, PTH levels and decreased vitamin D (р<0,001).

The research was carried out in accordance with the principles of the Helsinki Declaration. The study protocol was approved by the Local Ethics Committee of these Institutes. The informed consent of the patient was obtained for conducting the studies.

No conflict of interest was declared by the authors.